Modern automatic dishwashers generally include automatic control of in-flow of water from the water supply line into the machine. This automatic control is typically provided by a timer which causes a fill valve to be opened at the appropriate point in the machine cycle for a predetermined time interval, allowing water flow into the dishwasher tub during this interval. These "time fill" arrangements require close tolerances of both the timer mechanism and the water fill valve. That is, it is normally desirable to integrate the timing mechanism and the water fill valve such that the changes in line pressure, which vary with the time of day and from locality to locality, are adequately compensated to prevent overfill and/or underfill conditions. Overfill results in a waste of energy and underfill normally causes poor washing performance.
These automatic control arrangements taught by the prior art also create the possibility of a flooding condition being reached when water overflows from the tub and out of the machine which may cause damage. Such a flooding condition may occur for a variety of reasons, such as failure of the fill valve, over-pressure line conditions, a clogged dishwasher drain, etc. Many dishwasher designs accordingly provide for some arrangement for flood control. In some of these designs a failsafe mechanism is incorporated into the electrical control which will correct flood level conditions occurring during the machine cycle. Some failure modes, however, such as a mechanical failure of the valve, may occur at any time, not only during the machine operation.
Thus, it is desirable to have 24-hour flood protection. For example, in U.S. Pat. No. 3,894,555, a flood control feature is disclosed in which a float is mounted within the dishwasher tub which acts to deenergize a secondary electrically operated valve installed downstream from the fill valve. If a flood level occurs in the tub, the float rises to the flood level and acts to operate an associated switch to open the circuit to the secondary flood control valve, causing closing of the valve and cessation of the flow to the tub. The secondary valve however adds significantly to the expense of manufacture, since an additional relatively costly electrically operated valve is required. In addition, the reliability of electrically operated valves is less than mechanically operated valves and any failure of the valve will cause either malfunction of the dishwasher or defeat the flood control feature.
Accordingly, it is an object of the present invention to provide a mechanically operated level control arrangement for dishwashers.
It is a further object of the present invention to provide 24 hour flood control protection by terminating in-flow to the dishwasher tub whenever the level in the tub rises above a predetermined optimum washing level.
It is still a further object of the present invention to provide a level control feature which operates in a highly reliable manner, but does not substantially add to the cost of manufacture of the machine.
Another object of the present invention is to provide a level control for a dishwasher which is responsive to a predetermined optimum fill level for the dishwasher and which is operatively accurate regardless of line pressure variances.
A further object of the invention is to provide a level control arrangement for a dishwasher which can be easily incorporated in present dishwasher designs and through utilization of presently available parts requires only a minor modification.